The invisibility of Barnard's Star is a consequence of its being a red dwarf (spectral type M). Proxima Centauri, the host star of Proxima Centauri b, is also a red dwarf. Such stars are cool stars of low mass with a surface temperature of less than 4,000 K. In comparison, our Sun has a surface temperature of about 5,800 K. While Barnard's Star emits very little visible light, its emission in the short-wavelength infrared is considerable, as can be seen in the graph.

Brown dwarfs are failed stars in that they are too small to sustain hydrogen fusion. After forming, these failed stars slowly cool, contract, and dim over time.[2] Depending on its initial size, the temperature of a brown dwarf will range from as cool as a gas giant planet to nearly as hot as a star.[2] Knowledge of the distribution of brown dwarfs is important to the understanding whether they form in isolation, or whether they are ejected from planetary systems.[2]